1. Field of the Invention
The present invention relates to a novel, inexpensive, continuous process for the hydrogenation of esters of unsaturated fatty acids or ester mixtures of unsaturated fatty acids to give esters or ester mixtures of saturated or partially saturated fatty acids in which no undesirable higher monoalcohols or aldehydes which are characterized by an unpleasant odour or flavour are formed as by-products.
The hydrogenation of esters of unsaturated fatty acids or ester mixtures of unsaturated fatty acids allows compounds or compound mixtures having a higher or lower melting point to be prepared from the usually liquid unsaturated compounds.
From liquid vegetable or animal mixtures of glycerides of fatty acids, high-grade solid food fats can be produced in this manner which are extensively used as margarine or frying fats, but can also be used industrially (e.g. as lubricants).
2. Description of the Related Art
It is known to hydrogenate ester mixtures of unsaturated fatty acids discontinuously with hydrogen over Ni powder to give esters of saturated fatty acids (DRP 141 029).
It is further known to hydrogenate ester mixtures of unsaturated fatty acids discontinuously with hydrogen over mixed catalysts of the hydroxides, oxides or carbonates of Ni, Co, Fe with Cu or Pd, Pt or Ag to give esters of saturated fatty acids (U.S. Pat. No. 1,268,692).
It is further known to hydrogenate ester mixtures of unsaturated fatty acids semi-continuously with hydrogen in a plurality of series-connected discontinuous apparatuses using Ni powders or Ni on pulverulent kieselguhr as a support (GB 804 604, U.S. Pat. No. 2,932,658).
Moreover, it is known to hydrogenate ester mixtures of unsaturated fatty acids continuously with hydrogen on stationary Ni spirals located in a vertical column (GB 162 370, GB 203 218).
The course of the reaction can be illustrated, e.g. for the hydrogenation of methyl linoleate to give methyl stearate by the following reaction diagram: ##STR1##
In the known processes for the hydrogenation of esters of unsaturated fatty acids or ester mixtures of unsaturated fatty acids, dicontinuous suspension processes (batch processes) are almost exclusively used in which the esters of fatty acids or ester mixtures of fatty acids are hydrogenated with hydrogen over pulverulent, predominantly Ni-containing, catalysts.
Discontinuous processes have the disadvantage that their capacity is very small relative to the reaction volume and there is thus a requirement for large reaction apparatuses and storage tanks. Energy consumption and labour requirements are relatively high.
Continuous powder catalyst processes which employ a plurality of hydrogenation reactors connected in cascade avoid some of these disadvantages. However, there remains the requirement of specifically repeatedly dosing the pulverulent catalysts, circulating them by pumping and quantitatively filtering them off from the reaction product. The catalyst slurry pumps are subject to high mechanical wear. The quantitative removal of the pulverulent catalysts from the reaction product is complex. In addition, there is a great danger of relatively rapidly decreasing the catalyst activity by the additional operations. It is therefore advantageous to allow the reaction to proceed over fixed catalysts. Such catalysts must have a high activity which must not decrease over a relatively long period, because frequent changes of catalyst in fixed-bed reactions are likewise complex.
The hydrogenation of ester mixtures of unsaturated fatty acids on stationary Ni spirals (see above) situated in a vertical column has previously been described as a continuous process. However, such a process operates with low efficiency and has not proved itself in practice because the metallic Ni spirals have only a relatively low active surface area (&lt;1 m.sup.3 /g).